Study of the effects of quantum paraelectric on the structure and properties of Ferroelectric and multiferroic materials

Perovskite materials constitute an important class of functional materials due to their superior functional properties including piezo-/ferroelectricity and have attracted enormous research interest in materials science and engineering. The complex oxides of perovskite structure also exhibit intricate structure-property relations. The rising demands for advanced energy storage capacitors and electromechanical transducers in a wide range of applications require material scientists to prepare perovskite materials which not only exhibit good piezo-/ferroelectric performance but also provide wide working temperature and electric field ranges. The current commercially available piezo-/ferroelectric perovskite materials encounter some issues like lead toxicity, low energy storage capacity and a low coercive field, which needs to be resolved. This thesis work focuses on the study of the effects of a quantum paraelectric lead-free material on the structure and properties of three important categories of perovskite materials namely, lead-based PbZr1-xTixO3, lead-free BaTiO3 and multiferroics BiFeO3, with a view to gaining a better understanding of the structure-property relations in perovskite oxide solid solutions. Under this theme, novel quantum paraelectric-based complex perovskite solid solutions of (1-x)PbZr0.52Ti0.48O3 – xEuTiO3 (PZT52/48-ET), (1-x)BaTiO3 – xEuTiO3 (BT-ET), (1-x)Ba0.77Ca0.23TiO3 – xEuTiO3 (BCT-ET), Ba0.85Ca0.15-xEuxZr0.10Ti0.90O3 (BCEZT) and (1-x)BiFeO3 – xEuTiO3 (BF-ET) have been synthesized in the form of ceramics. The quantum paraelectric modified lead-based materials show high dielectric constant, high coercive fields, and enhanced piezoelectric properties. The lead-free materials modified by the quantum paraelectric ET exhibit diffuse phase transitions and relaxor ferroelectric behaviour, providing a wider working temperature range. The relaxor ferroelectric behaviour of these materials leads to the enhancement in the energy storage properties. Moreover, the multiferroic materials substituted with quantum paraelectric material show enhanced ferroelectric and ferromagnetic properties, making them true room-temperature multiferroic materials. These solid solution materials constitute new families of piezo-/ferroelectric and multiferroic materials potentially useful for electromechanical transduction, energy storage and spintronics applications. Furthermore, the structure-property correlations in the quantum paraelectric modified perovskite solid solutions, such as the crossover from ferroelectric to relaxor ferroelectrics, the crystal chemistry features between piezo-/ferroelectricity and the morphotropic phase boundary (MPB), are established. The comprehensive studies of the structures and dielectric, piezo-/ferroelectric and multiferroic properties of these materials provide guidance for the design and development of novel lead-reduced and lead-free high-performance piezo-ferroelectric and multiferroic materials in the future.